The skin which is a primary barrier of the human body protects organs in the body from change of temperature and humidity and stimulation from the outer environment such as UV rays and pollutants and plays an important role for homeostasis such as regulation of body temperature. However, excessive physical and chemical stimulation from the outside, UV rays, stress and malnutrition may deteriorate normal functions of the skin and promote skin aging such as elasticity loss, keratinization and wrinkle formation. Particularly, the dermis-epidermis junction is severely damaged by UV irradiation.
As a result of the observation of change in the skin by aging, it has been found that the change in the structure of the dermis-epidermis junction such as multiplication and heat insulation already begins in the skin exposed to UV rays from late twenties. Therefore, it can be expected that generation of gelatinase (MMP-2, MMP-9) is induced at the epidermis of the human skin exposed to UV rays and associated with the damage of the dermis-epidermis junction. Further, in the research using mouse wrinkle model induced by UV-B irradiation for a long period of time, it has been found that gelatinase formed in the epidermis by UV-B irradiation may cause damage of the dermis-epidermis junction, damage of dermis and wrinkle formation. Meanwhile, the skin which has been seldom exposed to UV rays does not show such multiplication and heat insulation even at the advanced age.
Gelatinase (MMP-2, MMP-9) is an enzyme to decompose type IV collagen, type VII collagen and other extracellular matrix which are components of the dermis-epidermis junction. According to the analysis according to Gelatine zymography and Enzyme Linked Immunosorbent Assay (ELISA), MMP-2 and MMP-9 are detected in the UV-exposed epidermis. The activity of gelatinase in the skin is detected near epidermal stratum basalis and stratum spinosum in the chilled forehead skin. Moreover, gelatinase is detected in the epidermis of the UV-exposed skin such as the face. Therefore, it is believed that UV rays induce formation of gelatinase in the epidermal stratum basalis, a part of them participates in destruction of the dermis-epidermis junction and the rest stays in the epidermis and reaches the epidermis.
Upon examination of the wrinkle formation mechanism in the wrinkle model produced by irradiating UV rays to a mouse for a long period of time, gelatinase activity is detected throughout the epidermis in the skin exposed to UV-B for a long period of time. The damage of the dermis-epidermis junction is observed from the fifth week of UV-B irradiation and becomes severe upon the seventh and tenth week. Upon the tenth week, heat insulation is observed in the dermis barrier and multiplication is observed in a part. Upon examination of collagen fiber of the dermal mammillary portion, reduction of fiber density is observed by UV-B irradiation for a long period of time. Therefore, it has been provided that the induced gelatinase is involved in damage of the dermis-epidermis junction and collagen decomposition of the mammillary dermis.
When the dermis-epidermis junction is damaged, wrinkle is formed by flattering of the junction, multiplication and heat insulation, and the skin is sagged and is apt to be damaged. Also, by the loss of the characteristic barrier function, the dermis-epidermis junction fails to filter pollutants from the outer environment, whereby noxious materials can readily infiltrate to the dermis and the skin can be damaged. In order to recover the damaged dermis-epidermis junction or maintain it at the healthy state, its components should be maintained as they are. The components which is known that whose biosynthesis is decreased, as the age increases, are type IV collagen, type VII collagen and laminin 10/11. Laminin 5 does not shown change while the components whose biosynthesis is increased are gelatinase (MMP-2 and MMP-9) which is known to be associated with decomposition (Lavker et. Al. J. Invest. Derm. 1979, 73:59-65, Pouliot et. Al. Exp. Dermatol. 2002, 11:387-397).
In order to prevent the skin aging by UV irradiation and outer stress and maintain healthy and elastic skin, there have been efforts to maintain peculiar function of the skin and activate skin cells to effectively inhibit the skin aging by using cosmetic composition supplemented with physiological activating materials obtained from animals, plants and microorganisms.